Metabolic biomarkers of Parkinson's disease.

Enzymic systems involved with metabolism of foreign chemicals, xenobiotics, have been studied in Parkinson's disease. Enzymes involved with sulphur oxidation and methylation are under-active. Cysteine levels are high and sulphate levels low. Differences in the activity of the enzyme monoamine oxidase-B are evident. Pathways involved with N-methylation of pyridines are different from controls leading to a rise in potentially toxic N-methylated derivatives.